This invention relates to a method for making a complex layer type lithographic printing plate which utilizes electrophotographic complex layer type photosensitive material and more particularly to a method for making a complex layer type lithographic printing plate wherein a charge carrier generating layer is soluble in an etching solution mainly composed of alcohol solvent and/or alkali solvent.
Hitherto, there have been used electrophotographic photosensitive materials which comprise a conductive support on which is provided, as a single layer, a photosensitive layer comprising charge-transport complexes of selenium, zinc oxide or polyvinyl carbazole and trinitrofluorenone as a photoconductor. However, recently, the so-called function-separated type electrophotographic complex layer type photosensitive materials where the function of carrier generation and that of charge carrier transport in the photosensitive layer are separated in two layers have been proposed and substances which have not been used because of low photosensitivity in the conventional single-layer photosensitive materials or novel substances which have not been known to have photosensitivity are used as charge carrier generating substances or charge carrier transport substances in electrophotographic complex layer type photosensitive materials. These complex layer type photosensitive materials are higher in sensitivity than said single-layer photosensitive materials.
Generally, the charge carrier generating layer of these electrophotographic complex layer type photosensitive materials is prepared by vacuum deposition of charge carrier generating substances per se or dispersing them in a suitable binder and making the dispersion into a thin layer. When the charge carrier generating substance is vacuum deposited, adhesion to a support or a charge carrier transport layer is low or even if there is no problem in the adhesion, solubility of the charge carrier generating layer in an etching solution mainly composed of alcohol solvent and/or alkali solvent is low. Thus, this cannot be applied to lithographic printing plates. On the other hand, when the charge carrier generating substance is dispersed in a binder, the binders are often insoluble in said etching solution and it is difficult to remove non-image areas. Even if a binder soluble in said etching solution is singly used, a long time is required for dissolving the binder or sensitivity is decreased. Thus, this cannot be applied to lithographic printing plates.